## [0645] Flashbacks

└ posted on Monday, 29 December 2014, by Novil

**Sandra:** Luna, you asked quite a few very weird questions in math today again.
**Luna:** … Sorry.

**Sandra:** Should I come over after school to help you study?
**Luna:** That would be very kind. Thank you.

**Sandra:** No problem. We all will get something out of it after all.
**Luna:** How so?

**Sandra:** The screams of terror of our old math teacher when you tried to factorize 49x² – 28 + 4 on the blackboard still haunt me every night.
**Luna:** The doctor said he may eventually be able to look at numbers again without getting flashbacks.

49x² – 24 or 49x² – 28x + 4?

Hello,

there is no = in the formular. I wanted to solve it … 🙁 … now I can’t.

Greetings

Juy Juka

@JuyJuka

It’s like jeopardy. Find the right question. 🙂

(What is (7x-2)²? )

@ JuyJuka:Try solving for “x”

Oops, didn’t see that it’s 28 and not 28x – solving for x gives a nice solution as well.

@ JuyJuka:Generally if there isn’t two sides to the equation you assume a “= 0” at the end.

@ Autoskip:Personally, I prefer to assume “= y”. A property that changes over the change in another property (such as velocity/time) is much more interesting than numbers that add up to zero. You can, however, then ask “at what time is velocity zero?”

An x was missing in the formula. I just fixed it.

I believe that X=.2916666666…etc. or as a fraction, 7/24

Forgive me if my quadratics are a little rusty.

7x-2 squared

Its

@ MawileCeyvis:Its not an equation, i see no = any where

@ MawileCeyvis:Sorry *y*. This is assuming that the above expression is = y. If not, then the best we can do is shorten it, which I probably could do but I’m to busy with nuzlocking pokemon platinum.

@ Noelwiz:…yeah, you’re right.

I don’t get it? Isn’t that already the expanded form of that polynomial?

Chill… They were asked to expand the expression, not solve for x… 🙂 BTW, the answer is (7x – 4)^2 .

@ Ajedi32:Wait… You’re right. It is expanded already. Shouldn’t it be “factor”?

x = pi/2, of course.

@ JuyJuka:You can still simplify it.

But umm, I’m not sure I understand the plot of this strip. Is the last panel on a different day?

@ MathAddict:(7x-2)^2

I feel like I should make a Harry Potter reference of some sort.

MathAddictwrote:Or rather they were given (7x – 2)² and asked to expand to get the answer 49x² – 28x + 4. as if the answer was (7x – 2)² that would be factoring not expanding 8)

Not sure what that means, but I guess she is really smart.

Wait that’s Trinomials! I know those but still don’t see the issue.

I don’t see how I can solve this without Einstein notation.

@ JuyJuka:Its not a one to solve… Expanding means the teacher wanted it simplified. In which case, it is easily (7x-2)^2.

fwtrumpwrote:Crap, I got that backwards, but same concept. I guess I got caught up in figuring out the original problem without putting much thought in what was being said.

@ Switch Master:it took me some thinking, but my guess is the expression is

alreadyexpanded as far as it can be (at least for any practical purpose) so there’s no point in expanding it further. How would you go about expanding it is bound to create an unnecessarily complex expression (such as x((5+2)x(3+4)-28)+4 , to come up with a “nice” one). and i’m guessing she jsut kept making it more and more complicated until the problem became unsolvable.For a computer analog, i’ve seen people who want to open Microsoft Word and have a Word icon on their desktop, one on their toolbar and one on their start menu, and yet feel the “simplest” way to get word to open is a path that takes them through Google

What sent the Teacher running way, screaming in Terror, is that she expanded it all the way into String Theory, then threaded the String through a Wormhole.

The power to cause PTSD in math teachers by expanding a math problem; I am liking Luna more and more!

Oh, and she finished up with: And from There, it becomes Obvious …

Well, we’re out of Time, so I’ll leave it as an exercise …

Geez, is she just confused, or trying to hard. I mean, to be able to give a math teacher PTSD when you’re actually working out a problem, she has to be trying in the wrong ways.

I just had memories of Pre-Calculus. The class that put me in my place regarding how good I was at mathematics. Interesting to see others expand it in the comments, though.

I am liking Luna and hope we see more of her; she has potential to be fun. (Even her name reminds me of Luna Lovegood and Princess Luna; two other characters I’ve always liked.) 🙂

Probably answered along the lines of ‘So as you take 28x away from 49x squared, you are left with 21x+4 is 25x. So x= 25.’ *Strangled noises in the background as the more competent students brains’ melt.

@ Iron Ed:LUNA! 😛

@ Karranor:DAMN YOU! THAT’S MY MATH YOU’RE DOING!

Do you know how long it’s been since I’ve had a good mathing?

If I wasn’t such a C student, I’d know what they are talking about

First step in reverse is (7x-2)(7x-2) =49x²-28x+4,

The x intercepts are (.7,0) and (-.7,0) the y intercept is (0,-24) which is also the vertex

The whole simplified equation is -4/7=7x²-4x and the table is

X. Y.

-3 417

-2 217

-1 25

0 -24

1 25

2 172

3 417

@ Crestlinger:Sadly, no. If only Maths was that easy. The thing is, its 49x squared, not 49x.

@ CDRom11:Actually, I think it’s “(49) x (X squared)”

Crestlingerwrote:First off your real answer is 85.75x=-4 from (49x*49x/28x)-4= (49x*1.75)-4=. But this Isn’t that type of math, it’s a multiple (infinity) solutions in this variable equation.

Second, Why did you assume 21x+4=25x when numbers off different variables can’t mix. You really have do your math right but all your steps are incorrect. Ps -4/21x is what second wrong step correction. Your heart may be pacing… or not but you could be steamed that I a student am not brain melting over your incorrect solution when there is no reasonable solution. For real and complete information look at my other comment.

darkrai444wrote:Sorry I meant 12.25x=-4… (7x*7x)=(49x*.25)-4.

Frankwrote:Ok so expanding means simplifying I guess, I never heard that term before. Also what logical sense does it make to open word via Google? Usually, I have my Wifi on my laptop off unless I need internet. I find clicking word on the desktop more convienent. Also what happens when there is no internet?

@ JuyJuka:it is simply a question of expansion so it is safe to assume that the missing right side is ” = 0″

Freiza – *Turns head* “Vegeta!! Explain!!”

Vegeta – (Laughs) “You see Freiza….you’re not dealing with the average math equation anymore, she has ascended beyond public school students, and become legend, the legend that you fear!!!”

No, honestly i have no idea what she’s wrote

It’s rather easy to do in your head as soon as you notice 49 is 7². Then everything else clicks out and you remember your old (a-b)² = a² – 2ab + b²…

I made the classical mistake and thought it was harder than it was, so instead of completing the square I put the expression equal to 0, to solve it and got the single solution x=14/49. That gave the factor form 49*(x – 14/49)^2. Then I simplified that to get (7x – 2)^2. I don’t like when I use a more complicated method than is necessary so solve a problem.

Now I can hear the teacher’s screams too! 🙁

Why do some of you guys assume a “=0” or “=y”? Thats no equation! If the teacher asks to factorize, you just need to make a step back in the “normal” way of calculating. It’s just “(7x-2)^2 = 49x^2-28x+4 the other way round! Some other people got that answer too, so believe them, please.

Fredwrote:Thank you Fred, that’s the perfect, general way! 🙂

I think Luna can be excused, you are definitely not required to be able to do this when you’re 13. I also think it works to her credit that she actually asked questions, even if they were weird. Normally the students who are bad at a particular subject keep their mouths shut which makes it harder to see what exactly they have a problem with.